Police in Bangladesh have detained two factory owners for criminal negligence over the deaths of at least 352 workers at an eight-storey building that collapsed on Wednesday – a day after warnings had been given that it was unsafe.

Two engineers who had been involved in issuing building permits for the Rana Plaza complex in Savar, just north of Dhaka, were also being held. The owner of the building was being sought by police, who have put border authorities on alert and arrested his wife in an attempt to bring him out of hiding.

On Saturday around 30 survivors were found and police say that as many as 900 people remain missing, trapped dead and alive under the twisted steel and concrete, through which rescue teams were still searching last night using electric drills, shovels, crowbars and their bare hands. Anger at the collapse has sparked days of protests and clashes, with police on Saturday using teargas, water cannon and rubber bullets on demonstrators who burned cars.

In London, demonstrators gathered outside Primark's flagship store in Oxford Street after it emerged that the chain used a floor of the Savar building. A petition has been launched calling for Primark and other brands, including Matalan and Mango, which used the factories, to compensate the families of workers killed or injured.

Murray Worthy, from the campaign group War on Want, said that it was not calling for a boycott that might cost jobs where they are badly needed in the impoverished Asian country: "We're here to send a message to Primark that the deaths in Bangladesh were not an accident – they were entirely preventable deaths. If Primark had taken its responsibility to those workers seriously, no one need have died."

Campaigners want Primark, Matalan and Mango to sign the Bangladesh fire and building safety agreement to end the "appallingly unsafe factory conditions" in the country.

After the owners of the New Wave Apparel and New Wave Bottoms factories, which had been on the sixth and seventh floors of the building, surrendered to police in the early hours of Saturday morning, a spokeswoman for Matalan, which has 212 stores in the UK, said: "We can confirm that New Wave has been a supplier to Matalan, although we don't have any current production with them." The arrests come after growing public anger over revelations that Sohel Rana, the politically connected owner of Rana Plaza, had been allowed to build the complex without permits, and that garment factory owners ordered workers into the building despite large cracks appearing in the walls, and jolts being felt at the structure the previous day.

As tens of thousands of workers continued to protest in the garment factory belts around Dhaka, the government has ordered all factories to remain closed until tomorrow. "These workers were called to their deaths by the owners," said Munir Hossain, a demonstrator in the Badda area of Dhaka. "This is not an accident. It's murder."

At the remains of the building, as wailing relatives pushed against a ring that volunteers had created around the site, engineers have been tunnelling through an adjoining building to reach the lower floors. Army officers co-ordinating the rescue teams, composed of soldiers, firemen and local volunteers, have said they are reluctant to use bulldozers until they are sure that there are no remaining survivors. But on Saturday, desperate cries were still being heard through cracks in the concrete. As dust-covered survivors were pulled out, waiting families cheered, the noise almost drowning out the sirens of the ambulances waiting to take them to hospital. "I was on the fourth floor when the floor suddenly gave way under me," said Nasima Banu, 25, a seamstress at Phantom Apparel, which lists Mango among its clients. "I was buried alive. I thought I would never see my husband and children again."

The disaster dwarfs Bangladesh's last industrial accident, a fire in November at the Tazreen fashions factory that killed more than 100 people. That accident brought promises of reform from the government and manufacturers, but analysts say nothing has changed in five months. Although around 700 workers have died in industrial accidents in Bangladesh since 2005, according to the International Labour Organisation, no factory owner has been found guilty of negligence. "The political clout of the garment industry makes reform difficult," said Babul Akter, the president of the Bangladesh Garment and Industrial Workers' Federation.

The Savar tragedy has increased pressure on a country already facing criticism for poor labour conditions. In December a group of US congressmen wrote to Barack Obama's trade representative, Ron Kirk, calling for a review of facilities enjoyed by Bangladeshi exporters. The US gives developing countries special tariffs to export goods to the US. But Bangladesh could lose preferential treatment. Bangladesh's garment industry was the third largest in the world in 2011, after China and Italy, and with a minimum wage of about $38 (£24) a month it draws international brands looking for a cheaper alternative to China.